OFFSET
1,1
COMMENTS
Primes p arising in A320442.
All terms but the first == 1 (mod 6).
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
367 is in the sequence because 367, 2*367-1=733, and 367733 are all primes.
MAPLE
filter:= proc(p) local q, r;
if not isprime(p) then return false fi;
q:= 2*p-1;
r:= p*10^(1+ilog10(q))+q;
isprime(r) and isprime(q);
end proc:
select(filter, [2, seq(i, i=7..200000, 6)]);
PROG
(PARI) isok(p) = isprime(p) && isprime(2*p-1) && isprime(eval(concat(Str(p), Str(2*p-1)))); \\ Michel Marcus, Jan 10 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, Jan 09 2019
STATUS
approved